Fluid seal for compressor



June 23, 1964 1.. B. SCHIBBYE 3,138,320

FLUID SEAL FOR COMPRESSOR Filed Jan. 14, 1960 3 Sheets-Sheet 1 IN VENTOR.

LAURITZ BENEDICI'US SCHIBBYE June 23, 1964 1.. B. SCHIBBYE FLUID SEALFOR COMPRESSOR 5 Sheets-Sheet 2 Filed Jan. 14, 1960 IN VEN TOR.

LAURITZ BENEDICTUS SCHIBBYE Wlf/ June '23, 1964 L. B. SCHIBBYE 3,138,320

FLUID SEAL FOR COMPRESSOR Filed Jan. 14, 1960 3 Sheets-Sheet 5 AWIWIIIz/WIl/V/l/IIIIIIIA F1" 5 J 7a IN V EN TOR.

LAURITZ BENEDICTUS SCHIBBYE United States Patent 3,138,320 FLUID SEALFOR COMPRESSOR Lauritz Benedictus Schihbye, Villa Stugan,Saltsio-Duvnas,

Sweden, assignor to Svenska Rotor Maskiner Aktiebolag, Nacka, Sweden, acorporation of Sweden Filed Jan. 14, 1960, Ser. No. 2,484 Claimspriority, application Sweden Jan. 15, 1959 9 Claims. (Cl. 230-143) Thisinvention relates to a screw rotor machine for operation as compressoror expander in a known manner comprising at least two co-operating maleand female rotors with intermeshing lands and grooves, a casing providedwith end walls and cylindrical bores for the rotors intersecting eachother, with substantially diagonally placed low pressure and highpressure ports. The machine further having nozzle means provided on thehigh pressure side of the machine for injection of a liquid underpressure, there being clearance provided between the rotors and thecasing which are formed so that at their revolving the rotors togetherwith the casing provide closed chambers consisting of communicatinggroove portions of two co-operating rotors and varying in volume as therotors revolve. Since such a machine would have a built-in pressureratio such that it could be utilized as a compressor or expander, itwould be advantageous to provide the same with at least three lands oneach rotor.

In earlier known embodiments of screw rotor machines of the type underconsideration nozzle means have been provided for injection of a liquidunder pressure into the chambers either axially through nozzle meanslocated in a low pressure end wall, in the transverse plane through eachof nozzle means located in the jacket walls of the easing or in therotors. The object of this liquid injection has been to improve thesealing between the cooperating rotors and between each rotor and thecasing. The rotors must be disposed in the casing so that a closetolerance between rotors and casing is obtained in order to preventdirect contact and resulting seizure.

The rotors in the previous types of dry operating compressor must bedesigned to operate with a similar close tolerance therebetween andtherefore must be fitted with synchronizing wheels to maintain thisclearance. However, by utilizing oil as injection liquid synchronizingwheels may be dispensed with and the female rotor directly driven by themale rotor. This results in the clearance between the front face of thelands of the male rotor and the back face of the lands of the femalerotor being eliminated. The clearance between the back face of the landsof the male rotor and the front face of the lands of the female rotor ismaintained in such a case. Besides said clearances between the axiallyextending surfaces of the casing and the rotors, clearances also must beprovided between the ends of the rotors and the end walls of the casing.At the high pressure end the pressure difference between both ends ofthe rotors is equal to the total pressure difference between thepressures in the high and low pressure ports resulting in a need forsealing of this clearance.

Through said clearances there is a continuous leakage from chambers ofhigher pressure to chambers of lower pressure. This leakage is dependenton the width and length of the clearances, the pressure diiferencebetween two adjacent chambers, the time and the properties of theworking medium. By injection of oil in the gas constituting the workingmedium these properties can be changed so that the leakage isconsiderably reduced while the working medium is also cooled so that thetemperature of the compressor will not become overly high and thethermal expansion becomes less thereby permitting narrower clearances.This enables the number of revolutions of the compressor to be reducedwhile maintaining its volumetric efficiency as well as increasing thecompression rate in each compressor stage.

Through investigation the manner in which liquid injection is performedhas been found to be most important. One object of the present inventionis the design and location of the injection nozzles to promote goodsealing between the rotors and casing. It is characteristic of thepresent invention that nozzle means be provided for injection of theliquid at an angle to the plane transverse to the axes of the rotors andthrough the respective nozzle means in the direction of the highpressure port. Thus the injection liquid obtains a component of movementcounterdirected to the gas flow along the walls of the casing because ofthe pressure dilference.

A further characteristic of the invention is that the nozzle means areprovided in the cylindrical walls of the casing on the same side of theplane through the axes of the rotors as the high pressure port andparticularly along the line of intersection between two adjacentcylindrical bores.

Those and other characteristics of the invention and the advantagesensuing therefrom will be apparent from the following description of anumber of embodiments shown in the accompanying drawing.

FIG. 1 is a vertical longitudinal section taken on line 1-1 in FIG. 2 ofa screw rotor compressor according to the invention.

FIG. 2 is a vertical cross section of this compressor taken on line 2-2in FIG. 1.

FIG. 3 is a modification of a detail in FIG. 2.

FIG. 4 is a further modification of a detail in FIG. 2.

FIG. 5 is a view of the end wall on the high pressure side of the casingtaken on the line 55 in FIG. 1.

FIG. 6 is a cross section of a detail of the end wall of the casingtaken on line 66 in FIG. 5.

FIG. 7 is a view of a modification of the end wall of the casing on thehigh pressure side taken in the same manner as in FIG. 6.

FIG. 8 is a longitudinal section through another embodiment of a screwrotor compressor.

FIG. 9 is a modification of same detail as in FIG. 5 taken on line 9-9in FIG. 10.

FIG. 10 is a detail in cross section taken on line 1010 in FIG. 9.

FIG. 11 is another detail in cross section taken on line 11-11 in FIG.9.

The screw rotor compressor according to FIGS. 1, 2 and 5 comprises twoco-operating rotors 20 and 22, of which one, the male rotor 20, isprovided with four convex lands 24 and intervening grooves 26 andco-operates with the other or female rotor 22 which is provided with sixconcave lands 28 and intervening grooves 30. The rotors 20, 22 arejournalled in end walls 32 and 34 of the casing 36 of the compressorwhich for the rest comprises a jacket 38 encircling the rotors. The highpressure end wall 32 is made integral with the jacket in the form of abarrel portion 38 while the low pressure end wall is made separate.

The casing is provided with an inlet 40 with a low pressure port 42 tothe working chamber 44 defined by the jacket 38 and the end walls 32 and34 and with an outlet 46 with a high pressure port 48 from the workingchamber 44 for the gas, for instance air, which is to be compressed inthe machine. The low pressure port 42 is entirely axially arranged andhas its opening edge 35 located radially inside the outer peripheries ofthe rotors to maintain a liquid film along the jacket wall 38. The lowpressure port 42 and the high pressure port 48 are placed approximatelydiagonally opposite each other in the working chamber 44. In the caseshown the low pressure port 42 is located upwardly and the high pressureport 48 downwardly in the casing 36. The invention,

however, is not limited to this placing but this can be varied accordingto known principles.

On the high pressure side along the intersection line between the twobores,'which provide the working chamber 44, the jacket 38 is providedwith a hollow space 52 having a supply opening 54 through which liquidis supplied under pressure from a source of pressure liquid, not shown.Between the hollow space 52 and the working chamber 44 a plurality ofpassages 56 are provided along said intersection line, of which passageseach one is directed at an oblique angle with respect to a transverseplane normal to the axes of the rotors through the mouth of the passage56 into the working chamber 44 in a direction toward the high pressureport 48 and serves as an injection nozzle for the liquid supplied to thehollow space 52 through the supply opening 54.

In the casing 36 a second hollow space 58 is provided adjacent the highpressure end wall 32. This hollow space is provided with a supplyopening 60 through which a liquid under pressure is supplied from asource of pressure liquid, not shown. Between the hollow space 58 andthe working chamber 44, as is evident from FIG. 6, a plurality ofpassages 62 are provided each of which is directed at an oblique anglewith respect to the plane of the end wall in a direction toward the highpressure port 48.

The machine operates in the following manner. Gaseous working mediumenters through the inlet port 42 into two communicating grooves 26, 30in the rotors 20, 22 on the low pressure side of the compressor. Thesetwo grooves form a suction chamber which is open to the inlet port andat its other end closed in that the lands 24, 28 leading in thedirection of rotation of the one rotor intermesh with the groove on theother rotor, the volume of which chamber successively increases as therotors revolve until the lands completely leave the grooves and insteadseal against the high pressure end wall 32 of the casing. Working mediumsimultaneously and continuously flows in and fills the chamber.

When the grooves 24, 26 have opened to their maximum size they areclosed relative the inlet port 42 in that two lands 24, 28 seal off thelow pressure port 42. Said lands 24, 28 during the continued revolvingof the rotors 20, 22 intermesh more and more and fill up the two grooves26, 30 lying in front thereof in the direction of rotationsimultaneously as to impart to the working medium a peripheral and axialmovement towards the high pressure port 48. When the lands 24, 28 haveclosed the chamber formed by the both communicating grooves 26, 30 acompression begins of the quantity of working medium enclosed therein inthat at the inlet end the lands 24, 28 more and more enter into thegrooves 26, 30 while at their high pressure ends the grooves are sealedby means of the high pressure end wall 34 of the housing.

By means of the compression the pressure on the working medium isincreased so that the latter tries to leak out through the clearancesbetween the rotors 2t), 22 and the casing 36 and also between the rotorsat their intermesh. This leakage acts as a gas flow in the directionfrom the high pressure port 48. In order to reduce this leakage liquidis injected into the working chamber 44 of the machine through thenozzles 56, 62. By this means the viscosity of the trapped workingmedium is altered so that the leakage is diminished. By means ofinjecting the liquid so that the liquid flow and the gas flow haveopposite directions of movement the gas stream is retarded and therebythe leakage is still more reduced. The axial flow becomes particularlyestablished within the range in which the lands 24, 28 and the grooves26, 30 intermesh on account of which the liquid in order to counteractthis flow preferably is injected at or adjacent to the line 50 ofintersection between the two bores which each encircles a rotor.

In order to reduce the leakage through the clearance 4- between the endsof the rotors and the high pressure end wall 32 of the housing, liquidis injected in the same manner in this clearance through the nozzles 62in a direction toward the high pressure port 48.

During the continued revolving of the rotors 20, 22 the chamber isopened towards the high pressure port 48 and the lands 24, 28 engagemore and more from the low pressure end with the grooves 26, 30 uponwhich the working medium under pressure is forced out from the machinethrough the outlet 46 to a liquid separator, not shown, for recoveringof the injection liquid which after cooling again by means of a pump,not shown, is injected into the machine.

Besides as sealing medium the injection medium serves as medium fordirect cooling of the working medium and possibly also as lubricantbetween the rotors. By utilizing lubricant oil as injection liquid andby supplying the same in sufiioient quantity the male rotor can when sois desirable directly drive the male rotor without interconnectingsynchronizing gears.

FIG. 3 shows another location of the passages between the hollow space52 and the working chamber 44. According to this embodiment thesepassages 64 are arranged in two parallel rows on both sides of theintersection line 50 between the both bores of the working chamber 44.This design is particularly suitable when the line 50 of intersectionsand the portion adjacent thereto must be made use of for other purposesor if the amount of injected liquid is too large to permit injectiononly through a single row of openings.

FIG. 4 shows still another location of the passages 66 between thehollow space 52 and the working chamber 44. According to this design thepassages are obliquely drilled in relation to the longitudinal plane ofsymmetry through the casing so that the passages 66 in the direction ofinjection incline towards the female rotor 22. This design of theinjection passages 66 is particularly advantageous in combination withrotor profiles which, in the case of the male rotor 20 consist ofsubstantially circular lands 24 located mainly outside the pitch circleof the rotor with intervening grooves 26, and which, in the case of thefemale rotor consist of substantially circular grooves 30 located mainlyinside the pitch circle of the rotor with intervening lands 28. Withsuch rotor profiles, blow openings are created along the intersectionline 50 from one chamber to the adjacent chamber through which a gasflow directed towards the male rotor 20 is created. To counteract thisgas flow it is advantageous to arrange the nozzles 66 for the fluidinjection so that the injected liquid jets are counterdirected to thisgas flow, viz. directed towards the male rotor in order to reduce theleakage created by this gas flow.

FIGS. 7 and 8 show an embodiment in which the injection passages 68 and70 are formed with increased inclination to the transverse plane themore nearly the high pressure port 48 the holes are located. By means ofthat is attained that in spite of the counter pressure increasingtowards the high pressure port 48 and the reduced absolute injectionvelocity of the liquid following therefrom, so can the velocitycomponent directed towards the gas flow be kept at constant size. Bymeans of this increasing inclination of the passages 68, 70 an equaleffective sealing can be obtained in the entire machine.

FIGS. 9 to 11 show another varied detail design. According to this openthe passages 72 in the high pressure end wall 32 into recesses 74 whichin the direction of injection are form-ed with increasing radial widthand decreasing axial depth. By means of these recesses 74 is attainedthat the jets of liquid ejected from the passages 72 when a rotor land24, 28 covers the passages 72 diverge in radial direction so that aliquid film covering the entire radial length of the rotor land 24, 28is created instead of a number of parallel separate liquid jets. Forthat reason seal-ing in this manner is obtained much more along theentire length of the rotor land 24, 28 than if the passages 72 hadopened into a smooth high pressure end surface 32.

While suitable embodiments of apparatus for carrying the principles ofthe invention into effect have been disclosed by way of example, it willbe understood that the invention embraces all forms of constructionfalling Within the scope of the appended claims.

I claim:

1. A compressor of the screw rotor type for compressing elastic fluidcomprising a casing structure providing a barrel portion havingintersecting bores with coplanar axes and confined by end wall portionsand further providing mainly diagonally located low pressure and highpressure ports communicating with said bores, male and female rotorsprovided with helical lands and intervening grooves rotatably mounted insaid bores, the lands of the male rotor having convexly curved flanksthe major portions of which lie outside the pitch circle of the malerotor and the grooves of the female rotor having concavely curved flanksthe major portions of which lie inside the pitch circle of the femalerotor, the lands and grooves of said rotors intermeshing to form withthe casing structure chevron shaped working chambers each composed ofcommunicating portions of a male rotor groove and a female groovejoining at the apex end of the chamber and said apex end moving axiallytoward said high pressure port as the rotors revolve to decrease thevolume of the chamber and effect compression of the fluid contentsthereof, and means for injecting liquid under pressure into the workingspace provided by said bores, said means comprising passages extendingthrough said casing structure on the high pressure side of the plane ofsaid axes and terminating at their inner ends in openings fordischarging liquid into said working space, said passages and openingsbeing constructed and arranged so that the liquid is discharged fromsaid openings obliquely with respect to a transverse plane normal to theaxes of said rotors in a direction giving the liquid discharge from saidopenings a velocity component directed towards said high pressure port.

2. A compressor as defined in claim 1 in which said means for injectingliquid comprises a plurality of passages extending through the wall ofthe barrel portion of said casing structure and terminating in openingslocated in the area adjacent to and inclusive of the line ofintersection between said bores on the high pressure side of said planeof the rotor axes.

3. A compressor as defined in claim 2 in which said openings aredisposed in two longitudinally extending rows each in a different one ofsaid bores and each adjacent to said line of intersection between thebores.

4. A compressor as defined in claim 2 in which said passages andopenings are constructed and arranged to discharge the liquid obliquelywith respect to a longitudinal central plane normal to the plane of saidaxes in a direction toward said female rotor.

5. A compressor as defined in claim 2 in which said' passages andopenings are constructed and arranged so that the liquid discharged froman opening nearer said discharge port is discharged at a greater angleof inclination with respect to said transverse plane toward said portthan is the liquid discharged from an opening more remote from saidport.

6. A compressor as defined in claim 1 in which said means for injectingliquid comprises passages and openings located in the high pressure endwall of said casing structure.

7. A compressor as defined in claim 6 in which said passages andopenings are constructed and arranged so that the liquid discharged froman opening nearer said discharge port is discharged at a gerater angleof inclination toward said port than is the liquid discharged from anopening more remote from said port.

8. A compressor as defined in claim 1, in which said openings are in theform of recesses of increasing radial width and decreasing axial depthin the direction of liquid flow through said openings.

-9. A compressor as defined in claim 2, in which additional means forinjecting liquid are provided, said additional means comprising passagesand openings located in the high pressure end wall portion of saidcasing structure.

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1. A COMPRESSOR OF THE SCREW ROTOR TYPE FOR COMPRESSING ELASTIC FLUIDCOMPRISING A CASING STRUCTURE PROVIDING A BARREL PORTION HAVINGINTERSECTING BORES WITH COPLANAR AXES AND CONFINED BY END WALL PORTIONSAND FURTHER PROVIDING MAINLY DIAGONALLY LOCATED LOW PRESSURE AND HIGHPRESSURE PORTS COMMUNICATING WITH SAID BORES, MALE AND FEMALE ROTORSPROVIDED WITH HELICAL LANDS AND INTERVENING GROOVES ROTATABLY MOUNTED INSAID BORES, THE LANDS OF THE MALE ROTOR HAVING CONVEXLY CURVED FLANKSTHE MAJOR PORTIONS OF WHICH LIE OUTSIDE THE PITCH CIRCLE OF THE MALEROTOR AND THE GROOVES OF THE FEMALE ROTOR HAVING CONCAVELY CURVED FLANKSTHE MAJOR PORTIONS OF WHICH LIE INSIDE THE PITCH CIRCLE OF THE FEMALEROTOR, THE LANDS AND GROOVES OF SAID ROTORS INTERMESHING TO FORM WITHTHE CASING STRUCTURE CHEVRON SHAPED WORKING CHAMBERS EACH COMPOSED OFCOMMUNICATING PORTIONS OF A MALE ROTOR GROOVE AND A FEMALE GROOVEJOINING AT THE APEX END OF THE CHAMBER AND SAID APEX END MOVING AXIALLYTOWARD SAID HIGH PRESSURE PORT AS THE ROTORS REVOLVE TO DECREASE THEVOLUME OF THE CHAMBER AND EFFECT COMPRESSION OF THE FLUID CONTENTSTHEREOF, AND MEANS FOR INJECTING LIQUID UNDER PRESSURE INTO THE WORKINGSPACE PROVIDED BY SAID BORES, SAID MEANS COMPRISING PASSAGES EXTENDINGTHROUGH SAID CASING STRUCTURE ON THE HIGH PRESSURE SIDE OF THE PLANE OFSAID AXES AND TERMINATING AT THEIR INNER ENDS IN OPENINGS FORDISCHARGING LIQUID INTO SAID WORKING SPACE, SAID PASSAGES AND OPENINGSBEING CONSTRUCTED AND ARRANGED SO THAT THE LIQUID IS DISCHARGED FROMSAID OPENINGS OBLIQUELY WITH RESPECT TO A TRANSVERSE PLANE NORMAL TO THEAXES OF SAID ROTORS IN A DIRECTION GIVING THE LIQUID DISCHARGE FROM SAIDOPENINGS A VELOCITY COMPONENT DIRECTED TOWARDS SAID HIGH PRESSURE PORT.